The forward, who was made available for transfer earlier this summer, has completed a temporary move to the Goldsands Stadium.
Lee played a pivotal role in helping Nigel Adkins’ men gain promotion out of League One, scoring 15 times and forming a prolific partnership with Rickie Lambert.
An unfortunate battle with injuries set Barnard back as he tried to force his way into the squad last season, which limited his Championship playing time.
With a good pre-season under his belt playing regularly in Saints’ Development Squad, Lee is on course to return to full fitness during his loan spell with the Cherries.
His signing means that he could be in contention for Bournemouth’s opening match of their League One season at Fratton Park this afternoon.