It's been a busy day for Leinster after the province also announced a raft of contract extensions.
Team captain Isa Nacewa has agreed to remain on for at least another season, while Irish internationals Dave Kearney, Jack McGrath, Mike McCarthy, Mike Ross, Rhys Ruddock and Tadhg Furlong are also among the 17 contract renewals that have been confirmed today.
Up-and-coming stars such as James Tracy, Garry Ringrose and Josh van der Flier have also been tied-down to new deals.
Along with Henshaw, Leinster have also announced the signing of former Munster forward Ian Nagle for next season - the second-row has just returned to professional rugby after taking an 18-month sabbatical.
In a further boost to Irish rugby, Ulster have announced that highly-rated back Stuart Olding has signed a contract extension that will keep him at Kingspan Stadium until the summer of 2019.
The 22-year-old has already won 39 caps for his native province as well as two caps for Ireland.
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