VETERAN Leeds forward Jamie Jones-Buchanan says his old second-row partner Gareth Ellis could hold the key to tomorrow's Ladbrokes Challenge Cup semi-final against holders Hull.

Ellis led Hull to their historic Wembley triumph over Warrington last August and, after missing ten matches in mid-season with a chest injury, has made a timely return as they seek to retain the trophy.

"I had the pleasure of packing down with Gaz in the back row for a lot of years," said Jones-Buchanan, who will make the 400th appearance of his career in the sold-out game at Doncaster's Keepmoat Stadium.

"He's a real competitor, a great winner and a nice lad as well. I think everybody, regardless of what club they play for, really loves Gaz Ellis and has got a heck of a lot of respect for him.

"When he came back from Australia, we were really keen to get him back here because we know what he can bring. He's world class as a back-rower and for any young kids out there wanting to learn to play back row certainly his career would be one to look at.

"He can change a game and having that presence in that team will lift everybody else. It's like Sean O'Loughlin in the Wigan team, it brings that extra ten to 15 per cent out in everybody else.

"Unlike me, he seems to be able to keep his cool on the pitch when he's challenged. He's a great professional and he'll have that mental and physical ability to lead his team this week and make them really strong."

Hull realised years of ambition with their victory at Wembley and Jones-Buchanan knows from experience how determined they will be to hang on to the trophy.

"They've had a taste of that forbidden fruit and, having galvanised themselves with that experience, I think they'll want that taste again," said Jones-Buchanan, who won the cup in 2014 but missed the Rhinos' successful trophy defence through injury. "It makes them dangerous without a doubt."

Ellis, 36, whose side return to the scene of their impressive semi-final win over Wigan 12 months ago, insists Hull are as hungry as ever to play again at Wembley.

"I definitely think so," he said. "It was unbelievable last year for the whole club, and the lads speak about it to this day. There are pictures on the wall that ensure the memory will live with us forever.

"It's another opportunity for us to show that we've really come on as a club. Consistency has always been an issue for Hull since I can remember, it's something we've been working towards in the last few years and a semi-final (win) over Leeds would go a long way to achieving that.

"That Wigan game last year was probably the best we've played and we certainly need to be at that level again. We've come unstuck against Leeds in recent years, even as recently as a couple of weeks ago, but if we bring our best game, I think we will be there or thereabouts."

Leeds, who have won their last eight meetings with the Black and Whites, are appearing in a record-equalling 47th Challenge Cup semi-final and are desperately hoping to send long-serving half-backs Danny McGuire and Rob Burrow out on a high this year.

Ellis has fond memories of his time at Headingley but insists friendships will be cast to one side for 80 minutes tomorrow.

"Obviously I've some great friends there but you want to get out there and get one over on them," he said. "You want to prove you've moved on but you're still doing all right.

"I want the best for Danny and Rob because they're good friends of mine but they've won enough I'd say, they've won a lot more than me for sure.

"I'm a Hull player now, I've been here for nearly five years and it almost feels like home. Also for me personally, I don't know when these opportunities are going to come around again. This could be the last."