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And he admitted a meeting with London Irish director of rugby Brian Smith was key to his decision.
"Moving down to London Irish is a fantastic opportunity for me," said the 31-year-old.
"Having met with Brian, discussed the vision of the club and seen the new training facility it was clear to see the intent the club has moving forward."
Smith meanwhile, is convinced Cross will improve his squad next season.
"It is great to have a player of Geoff's talent and experience," he added.
"He is a genuine international tight-head who has performed exceptionally well in the recent RBS 6 Nations Championship.
"We will have plenty of competition in the front row next season that will only benefit the squad."